1. Field of the Invention
The present invention relates to an inkjet printing apparatus that prints an image using ink supplied via an ink supply line from an ink tank, and also to a method of controlling such an inkjet printing apparatus.
2. Description of the Related Art
Among inkjet printing apparatuses that print an image onto a print medium by using a print head able to eject ink, there are apparatuses that supply ink to a print head via a tube or other ink supply pipe from an ink tank located at a position distanced from the print head. The inkjet printing apparatus that supplies ink via such an ink supply pipe has advantages such as increased freedom in ink tank placement, or easier enlargement of ink tank volume. However, since most elastic materials used for ink supply pipes have gas permeability properties, there is a risk that air bubbles may penetrate inside an ink supply pipe over long periods of use. In the case where such air bubbles accompany the flow of ink and flow into the interior of a print head, there is a risk of causing faulty ink ejection or other negative effects in the print head. For this reason, it is necessary to eliminate air bubbles that have penetrated into an ink supply pipe in this way.
As one method of discharging air bubbles inside an ink supply pipe, Japanese Patent Laid-Open No. H08-207315 (1996) describes a method that uses a configuration wherein ink inside a print head is forcibly suctioned out and discharged from a print head nozzle (a suction discharge operation). Namely, the elapsed time since the last suction discharge operation is measured, and the next suction discharge operation is performed when the measured time exceeds a fixed value. In so doing, air bubbles inside a print head are suctioned out and discharged together with ink.
In Japanese Patent Laid-Open No. H08-207315 (1996), only air bubbles that have permeated the material of an ink supply line are considered, and by managing time using a timer, air bubbles that have permeated and penetrated the material of the ink supply line are suctioned and discharged every time a fixed amount of time elapses. For this reason, the air bubble penetration volume cannot be ascertained with regard to air bubbles that are pushed in during ink tank installation or air bubbles whose penetration volume cannot be uniformly managed by time management only, and timings at which to perform suction discharge operations cannot be optimally set.